1. Field of the Invention
The present invention pertains to photoimaging and, in particular, the use of photoresist compositions (positive-working and/or negative-working) for imaging in the production of semiconductor devices. The present invention also pertains to photoresist compositions containing polymer compositions having high UV transparency (particularly at short wavelengths, e.g., 157 nm or 193 nm) which are useful as the film forming resin in a resist composition.
2. Background
In the process for manufacturing semiconductor devices, very fine features are etched onto a substrate, typically a silicon wafer. The features are formed on the substrate by electromagnetic radiation which is impinged, imagewise, on a photoresist composition applied to the silicon waver. Areas of the photoresist composition which are exposed to the electromagnetic radiation change chemically and/or physically to form a latent image which can be processed into an image for semiconductor device fabrication. Positive working photoresist compositions generally are utilized for semiconductor device manufacture.
The photoresist composition is applied to the silicon wafer by spin coating. The silicon wafer may have various different material layers applied to it in other processing steps. In addition, in a particular photolithographic processing step, the silicon wafer may have a hard mask layer, typically of silicon dioxide or silicon nitride, applied below the photoresist composition layer. In addition, an antireflective layer (ARC) may be applied below the photoresist composition layer, by a coating process (and is then typically referred to as a bottom anti-reflective (BARC)) or on top of the photoresist composition layer (and typically called a top anti reflective layer (TARC)). Typically the thickness of the resist layer is sufficient to resist the dry chemical etch processes used in transferring a pattern to the silicon wafer.
Various polymer products for photoresist compositions have been described in Introduction to Microlithography, Second Edition by L. F. Thompson, C. G. Willson, and M. J. Bowden, American Chemical Society, Washington, D.C., 1994.
The photoresist composition generally comprises a film forming polymer which may be photoactive and a photosensitive composition that contains one or more photoactive components. As described in the Thompson et al. publication, upon exposure to electromagnetic radiation (e.g., UV light), the photoactive component acts to change the Theological state, solubility, surface characteristics, refractive index, color, electromagnetic characteristics or other such physical or chemical characteristics of the photoresist composition.
The use of ultraviolet light of lower wavelength corresponds to higher resolution (lower resolution limit). Lithography in the UV at 365 nm (I-line) is a currently established image-forming process for making semiconductor devices. The features formed by this process have a resolution limit of about 0.35-0.30 micron. Known photoresist compositions for lithography using a 365 nm wavelength are made from novolak polymers and diazonaphthoquinones as dissolution inhibitors. Lithography in the deep UV at 248 nm has been found to have a resolution limit of approximately 0.35-0.13 micron. The known photoresist compositions for this process are made from p-hydroxystyrene polymers. Lithographic processes using electromagnetic radiation at even shorter wavelengths are looked to for forming very fine features because the use of lower wavelengths correspond to higher resolution; that is, in deep (wavelength less than 300 nm), vacuum (wavelength less than 200 nm) or even the extreme (wavelength less than 30 nm) ultraviolet. However, at wavelengths of 193 nm or shorter, the photoresist compositions known for use at 365 nm and 248 nm have been found to lack sufficient transparency.
A key difficulty encountered in developing polymers for use in photoresist compositions that are imaged at lower wavelengths, e.g., 157 nm, is the lack of transparency at these low wavelengths. The transparency requirements for photoresist compositions are usually on the order of allowing less than about 20 to about 40% of incident light to penetrate the fill thickness of the resist layer to produce an image with well-defined, vertical, side walls which are important in achieving high resolution and minimizing defects. Polymers which lack transparency absorb too much light and thereby produce an unacceptable image with low resolution and too many defects.
Because photolithography at the shorter wavelengths would provide the very fine features having lower resolution limits; that is, a resolution limit of approximately 0.18-0.12 micron at 193 nm, approximately 0.07 micron at 157 nm photoresist compositions that will be sufficiently transparent at these short wavelenths are needed.
There is a need for suitable photoresist compositions for use at 193 nm and lower, particularly at 157 nm, that have not only high transparency at these short wavelengths but also other key properties including good plasma etch resistance, good developability, and good adhesive properties.